Gold catalysts supported on TiO2 and TiO2/SiO2 were used in gas-phase propene epoxidation with a hydrogen−oxygen mixture. The catalysts were characterized by 197Au Mössbauer absorption spectroscopy (MAS), X-ray
photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Gold particle sizes of 1 wt
% Au catalysts calcined at 673 K ranged from 3 to 6 nm. Two Au contributions were found in Mössbauer
spectra and assigned to bulk metallic Au atoms in the core of a gold particle and metallic gold on the outer
surface of this particle. By MAS, no evidence for charge transfer from support to Au particle could be found.
The Auger parameters confirmed that the surface layer of 3−5 nm gold particles is metallic. Deactivation is
not due to a change in the active gold species but is related to the TiO2 support. In the preparation via
deposition-precipitation, Au(OH)3 species are converted to metallic gold during calcination. Gold particles
do not gradually grow during calcination, possibly due to the simultaneous conversion of Au(OH)3 moieties
with dehydroxylation of the TiO2 support. Epoxidation activity increases with the amount of surface metallic
gold. No evidence for oxidized gold under reaction conditions was found.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.